A fulfillment center is a materials handling facility that is equipped to store inventory and fulfill orders from the inventory. A variety of tasks may be performed in the fulfillment center including, for example, receiving shipments of new inventory, storing new inventory in storage locations, picking items from the inventory storage locations in response to receiving orders, grouping the picked items, packing the items, and readying the packed items for shipment. Sometimes agents performing a first type of task may work faster than agents performing a second type of task that follows the first type of task. As a consequence, items resulting from the first type of task may build up in a storage area of the fulfillment center until they can be processed in the second type of task.